SwiftUI Interview Questions And Answers: Part 1

7 min readJan 25, 2023

SwiftUI is a modern, flexible, and easy-to-use framework for building user interfaces on Apple platforms. It is the future of iOS and macOS app development, and it is becoming increasingly popular among developers.

I’ve compiled a list of the most frequently asked SwiftUI questions, along with clear and concise answers, to help you understand the concepts and best practices behind the framework.

Let’s dive in!

All questions featured in this article are sourced from the Uplift iOS Interview guide, with accompanying code examples accessible in the Ace iOS Coding Interview guide. If you find the article valuable, consider following me on LinkedIn and Twitter, where I regularly share iOS-related tips and tricks every week.

What is the difference between a State and a Binding in SwiftUI?

A State is a property wrapper that allows you to read and write a value, while a Binding is a property wrapper that allows you to read and write a value and also share it with other views.

What is the role of the body property in a SwiftUI view?

The body property is the main content of a view and it’s the only required property in a view. It defines what the view should display.

What is the difference between a Text and a Label in SwiftUI?

A Text is a low-level text view that can be customized with various text styles and attributes, while a Label is a higher-level text view that uses a standard font and text color by default.

What is the difference between a List and a ScrollView in SwiftUI?

A List is a container view that presents rows of data arranged in a single column, while a ScrollView is a container view that presents content in a scrollable viewport.

How do I use @State and @Binding in SwiftUI?

@State is used to create a state property that can be read and written to, while @Binding is used to share a state with another view.

How do I handle user input and gestures in SwiftUI?

SwiftUI uses the target-action pattern to handle user input and gestures. To handle user input, you can use the onTapGesture and onLongPressGesture modifiers on views, and to handle gestures, you can use the gesture modifier on views.

How do I implement navigation in SwiftUI?

SwiftUI uses a navigation view to implement navigation. To push a new view on the navigation stack, you can use the navigationBarItems and navigationBarTitle modifiers on views.

What is the difference between a @StateObject and an @ObservedObject in SwiftUI?

@StateObject and @ObservedObject share similar traits but diverge in how SwiftUI handles their lifecycles. Utilize the state object property wrapper to maintain consistency when the current view initializes the observed object. Whenever you inject an observed object as a dependency, employ the @ObservedObject annotation.

How to implement data binding in SwiftUI?

SwiftUI uses the @Binding property wrapper to implement data binding. You can use the $ operator to create a binding to a state property and pass it to another view.

What is the Combine framework?

The Combine framework is a reactive programming framework introduced by Apple in iOS 13, macOS Catalina, and watchOS 6. It provides a declarative Swift API for processing asynchronous events and streams of data, such as user input, network responses, and other types of events.

What are publishers and subscribers in the Combine framework?

In the Combine framework, a publisher is an object that emits a stream of values over time, while a subscriber is an object that receives and processes those values. Publishers and subscribers are connected through a subscription, and the subscriber can also cancel the subscription at any time.

How does Combine handle errors?

Combine provides a special type of publisher called a Failed publisher which can be used to emit errors. Subscribers can handle errors by providing a catch block in the sink method.

What is the difference between `merge` and `zip` operators in Combine?

The merge operator combines multiple publishers into a single publisher by emitting all the values from each publisher in the order they are received, while the zip operator combines multiple publishers into a single publisher by emitting a tuple of the latest values from each publisher in the order they are received.

How can you debounce events in Combine?

You can use the debounce operator to debounce events in Combine. It takes a dueTime parameter which determines the duration to wait before emitting the latest value.

How can you filter values in a stream using Combine?

You can use the filter operator to filter values in a stream. It takes a closure that returns a Boolean indicating whether the value should be included in the stream.

What is the `assign(to:on:)` operator in Combine?

The assign(to:on:) operator is used to bind the output of a publisher to a property on an object. It takes two parameters: the property to bind to and the object to bind to.

Can you explain the `share()` operator in Combine?

The share() operator allows multiple subscribers to attach to a single publisher, and it will only subscribe to the upstream publisher once. This can be useful for reducing redundant work, such as multiple network requests.

How can you combine multiple streams of data using Combine?

Combine provides several operators such as combineLatest, merge, and zip to combine multiple streams of data. combineLatest emits a value when any of the input publishers emit a value, merge combines multiple publishers into a single publisher by emitting all the values and zip combines multiple publishers into a single publisher by emitting a tuple of the latest values from each publisher in the order they are received.

Can you explain the `receive(on:)` operator in Combine?

The receive(on:) operator is used to specify the scheduler on which the subscriber will receive events. It takes a parameter of type Scheduler, which can be used to schedule the reception of events on a specific thread or queue. This is useful for ensuring that updates to the user interface are made on the main thread, for example.

How to handle errors in SwiftUI?

SwiftUI uses the Result type to handle errors. You can use the try? and try! operators to handle errors, or you can use the Result type to handle errors explicitly.

What is the role of the environment in SwiftUI?

The environment is a way to pass data and settings down the view hierarchy in SwiftUI. You can use the environmentObject() and environment() modifiers to set values in the environment.

How to create a custom view in SwiftUI?

To create a custom view in SwiftUI, you can create a new struct that conforms to the View protocol and define its body property. You can also use the custom modifier to customize the appearance of a view.

How to use the PreviewProvider in SwiftUI?

The PreviewProvider is a protocol that allows you to see a live preview of your views in Xcode. To use the PreviewProvider, you can create a struct that conforms to the PreviewProvider protocol and define its previews property.

How does SwiftUI handle data flow and state management?

SwiftUI uses a declarative approach to data flow and state management, where the developer declares the desired state, and the framework updates the view accordingly. The main tool for this is the @State property wrapper, which allows the developer to declare a variable as the source of truth for a specific piece of the user interface.

How can you create a custom layout in SwiftUI?

To create a custom layout in SwiftUI, you can use the GeometryReader view, which provides access to the size and position of its parent view, and the position and size properties of its children. You can also use the frame and offset modifiers to adjust the position and size of views.

How can you create a custom modifier in SwiftUI?

To create a custom modifier in SwiftUI, you can define a new ViewModifier struct and use it with the modifier() method. The struct should contain a single method called body, which returns the modified view. You can also use the environment property to pass custom data to the modifier.

What is the difference between a struct and a class in SwiftUI?

In SwiftUI, structs are value types and classes are reference types. This means that structs are copied when they are passed around, while classes are passed by reference. This can have implications for performance and memory usage, and it’s important to choose the right type for your needs.

How can you use animations in SwiftUI?

SwiftUI provides several animation functions such as animation(), withAnimation(), transition() and matchedGeometryEffect() that can be used to animate views. You can also use the animatableData property to create animatable properties in your custom views.

How can you use gestures in SwiftUI?

SwiftUI provides several gesture functions such as tapGesture(), longPressGesture(), dragGesture() and rotationGesture() that can be used to add gesture recognition to views. Each function takes a closure that is called when the gesture is recognized, and provides access to gesture data such as the location and movement of the user’s finger.

How can you use Core Data with SwiftUI?

To use Core Data with SwiftUI, you need to create a NSManagedObjectContext object and pass it to the Environment through the @Environment property wrapper. You can then use the FetchRequest struct to fetch the data, and the @FetchRequest property wrapper to bind it to a view.

How can you use SceneDelegate with SwiftUI?

To use SceneDelegate with SwiftUI, you need to set the window property of the UIWindowSceneDelegate to a UIHostingController that contains your SwiftUI view hierarchy. You can also use the UIWindowSceneDelegate to handle state restoration and other scene-related tasks.